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    <TITLE>package org.geotools.referencing.operation.projection</TITLE>
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  Basic implementations of {@linkplain org.geotools.referencing.operation.projection.MapProjection
  map projections}. This package is mostly for internal purpose and should usually not be used
  directly. Consider using {@link org.opengis.referencing.operation.MathTransformFactory} instead.

  <H3>Axis units and orientation</H3>
  <P ALIGN="justify">Many {@linkplain org.opengis.referencing.crs.GeographicCRS geographic coordinate reference systems}
  use axis in (<var>latitude</var>,<var>longitude</var>) order, but not all. Axis order, orientation
  and units are CRS-dependent. For example some CRS use longitude values increasing toward
  {@linkplain org.opengis.referencing.cs.AxisDirection#EAST East}, while some others use longitude
  values increasing toward {@linkplain org.opengis.referencing.cs.AxisDirection#WEST West}. The axis
  order must be specified in all CRS, and any method working with them should take their axis order and
  units in account.</P>

  <P ALIGN="justify">However, map projections defined in this package are <strong>transformation steps</strong>,
  not final CRS. All projections defined in this package must complies with the OGC 01-009 specification. This
  specification said (quoting section 10.6 at page 34):</P>

  <BLOCKQUOTE><P ALIGN="justify">
  Cartographic projection transforms are used by projected coordinate reference systems to map geographic coordinates
  (e.g. <var>Longitude</var> and <var>Latitude</var>) into (<var>X</var>,<var>Y</var>) coordinates. These
  (<var>X</var>,<var>Y</var>) coordinates can be imagined to lie on a plane, such as a paper map or a screen.
  All cartographic projection transforms will have the following properties:</P>
  <UL>
    <LI>Converts from (<var>Longitude</var>, <var>Latitude</var>) coordinates to (<var>X</var>,<var>Y</var>).</LI>
    <LI>All angles are assumed to be decimal degrees, and all distances are assumed to be meters.</LI>
    <LI>The domain should be a subset of {[-180,180)&times;(-90,90)}.</LI>
  </UL>
  <P ALIGN="justify">Although all cartographic projection transforms must have the properties listed above,
  many projected coordinate reference systems have different properties. For example, in Europe some projected
  coordinate reference systems use grads instead of decimal degrees, and often the base geographic coordinate reference
  system is (<var>Latitude</var>, <var>Longitude</var>) instead of (<var>Longitude</var>, <var>Latitude</var>).
  This means that the cartographic projected transform is often used as a single step in a series of transforms,
  where the other steps change units and swap ordinates.</P>
  </BLOCKQUOTE>

  <P ALIGN="justify">The Geotools implementation extends this rule to axis directions as well, i.e.
  (<var>X</var>,<var>Y</var>) coordinates must be ({@linkplain org.opengis.referencing.cs.AxisDirection#EAST East},
  {@linkplain org.opengis.referencing.cs.AxisDirection#NORTH North}) orientated. This rule implies a non-intuitive
  behavior for the <cite>Transverse Mercator South Orientated</cite> projection, which still projects coordinates
  with <var>Y</var> values increasing toward North. The real axis flip is performed by the rest of the CRS framework
  upon {@linkplain org.opengis.referencing.cs.CoordinateSystemAxis coordinate system axis} inspection. In order to
  get a real South orientated projection, the cartographic transform must be concatenated with an affine transform.
  This is done automatically if the {@linkplain org.opengis.referencing.crs.ProjectedCRS projected CRS} is created
  with the Geotools's {@link org.geotools.referencing.factory.FactoryGroup#createProjectedCRS createProjectedCRS}
  convenience method with a South orientated {@linkplain org.opengis.referencing.cs.CoordinateSystem coordinate system}
  in argument.</P>

  <P ALIGN="justify">In order to reduce the risk of confusion, this package never defines south orientated
  {@link org.geotools.referencing.operation.projection.MapProjection} implementations. The providers always
  create south-orientated projections as a concatenation of their north-orientated variants with an affine
  transform. This approach removes all ambiguity when reading a transform in
  <A HREF="http://geoapi.sourceforge.net/snapshot/javadoc/org/opengis/referencing/doc-files/WKT.html"><cite>Well
  Known Text</cite> (WKT)</A> format, since only the north-orientated variant is used and the affine transform
  coefficients tell exactly which axis flips are applied.</P>
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